1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic tape and magnetic disc.
2. Description of the Prior Art
A coating type magnetic recording medium, which comprises a substrate and a magnetic layer formed on a substrate by applying a magnetic paint on the substrate followed by drying, is widely used since it has a good handling property and mass productivity so that it is suitable for production on an industrial scale.
For improving recording characteristics of the coating type magnetic recording medium, various proposals have been made to add a larger amount of magnetic powder as a magnetic recording element to the magnetic layer, or to more homogeneously disperse the magnetic powder in the magnetic layer. As a result, output characteristics, particularly electromagnetic conversion characteristics have been improved.
During the use of a video tape or a floppy disc, however, the homogeneously contained magnetic powder in a large amount in the magnetic layer is scraped off from the surface by a magnetic head with which the magnetic layer is slidingly in contact, whereby the output characteristics and the electromagnetic conversion characteristics are deteriorated.
To prevent the scraping of the magnetic powder, abrasion particles having greater hardness than the magnetic head and the magnetic powder are added to the magnetic layer and, if desired, a liquid lubricant is additionally used. Such techniques are disclosed in Japanese Patent Publication Nos. 18572/1973, 15003/1973, 28642/1977, 49961/1977, 15771/1980, 24171/1980 and 51171/1982 and Japanese Patent Kokai Publication (unexamined) Nos. 466/1972, 56404/1973, 115510/1974, 62604/1975, 92101/1975, 93405/1975, 147308/1975, 31201/1976, 45309/1977, 75410/1977, 88307/1977, 97709/1977, 97710/1977, 16605/1978, 47806/1978, 134407/1978, 21805/1979, 103005/1979, 143608/1979, 1638/1980, 17811/1980, 17813/1980, 17814/1980, 17835/1980, 129935/1980, 150131/1982, 159236/1983 and 144036/1984.
However, the addition of the non-magnetic materials , such as the abrasive and the lubricant which do not contribute to magnetic recording, to the magnetic layer not only decreases the volume ratio of the contained magnetic powder in the magnetic layer, but also makes it difficult to homogeneously disperse both the magnetic powder and the nonmagnetic materials. That is, when the magnetic powder alone is dispersed in a binder resin of the magnetic layer, only the dispersibility of the magnetic powder is taken into consideration. When the non-magnetic materials, for example, the abrasive particles are used, they should be dispersed in the binder resin in addition to the magnetic powder. In such a case, when a mixing ratio of the magnetic powder and the non-magnetic materials is kept constant in the magnetic layer, the magnetic characteristics become non-uniform in the magnetic layer and in turn the output characteristics fluctuate.
Therefore, recently it is desired to provide another way to achieve both good output characteristics and durability of the magnetic recording medium at a high level.